1. Field of the Invention
The present invention relates to an imaging apparatus and an imaging system.
2. Description of the Related Art
In recent years, radiation imaging apparatuses including a flat panel detector (hereinafter abbreviated as “FPD”) formed of a semiconductor material have started to be put to practical use as photographing apparatuses that are used for medical diagnostic imaging or nondestructive inspection using X-rays. The radiation imaging apparatuses that use an FPD are capable of digital photographing in which radiation such as X-rays that were transmitted through a subject such as a patient are converted into analog electrical signals at the FPD, and the analog electrical signals are subjected to analog-to-digital conversion to acquire digital image signals. The FPDs that are used in such radiation imaging apparatuses are broadly divided into direct-conversion type FPDs and indirect-conversion type FPDs. A direct-conversion type radiation imaging apparatus includes an FPD in which a plurality of pixels that include a conversion element made using a semiconductor material, such as a-Se, that is capable of converting radiation directly into an electric charge are arranged in a two-dimensional shape. An indirect-conversion type radiation imaging apparatus includes an FPD in which a plurality of pixels that include a conversion element having a wavelength converter such as a phosphor that can convert radiation into light and a photoelectric conversion element made using a semiconductor material such as a-Si that can convert light into an electric charge are arranged in a two-dimensional shape. Such radiation imaging apparatuses that include an FPD are used, for example, in medical diagnostic imaging as digital imaging apparatuses for still image photographing like general photographing or moving image photographing such as fluoroscopy. In X-ray photographing, AEC (automatic exposure control) is used so that the amount of X-rays transmitted through a subject is within a photographing range that can be detected by a radiation imaging apparatus and also to suppress to the minimum the amount of X-ray exposure of a subject.